The invention relates generally to electrical machines and in particular, to a system and method of monitoring health of electrical machines.
Generally, an electrical machine such as power generator or motor is routinely monitored for proper maintenance and high efficiency during operation. One of the few aspects of monitoring health of the electrical machine is inspecting stator bar windings to ensure the windings are motionless during the operation. Typically, an electrical machine includes a wedge system to induce a radial retaining force to a stator to facilitate reducing movement of the stator bar windings within a stator slot. Such a wedge system may also include ripple springs embedded in the stator winding assembly. The ripple springs are generally in a state of compression to keep the windings from moving. However, if the wedge system becomes loose, the amount of retaining force is reduced such that the stator bar windings may move during operation. Over time, the relative motion of the stator bar windings causes damage to the insulation surrounding the stator bar wedges and a potential stator bar winding failure can occur. This may result in electrical shorts to ground, thereby, diminishing the efficiency of the machine and further decreasing the mean time between failures of the electrical machines. Accordingly, monitoring the health of the electrical machine is periodically carried out to determine if any stator bar winding movement within the stator slots exceeds predetermined tolerances.
Currently, several methods and systems are used for monitoring the health of the electrical machine such as the stator wedge tightness. These include applying steady or impulsive physical force to the stator wedge winding assembly and analyzing deflection, applying an excitation signal and analyzing the vibratory response, measuring the profile of the compressed ripple spring in situ and inferring the state of compression, or installing various sensors along the ripple spring that produce signals that may be correlated to the spring's state of compression. However, the aforementioned methods for determining the tightness of the wedge require offline measurements while the generator is not operational and do not predict the onset of loose wedges. Further, these current methods require either undue laborious or time-consuming effort to adjudge the tightness of an individual stator wedge assembly or they require calibration of a sensor that is proximate to a ripple spring but not an integral part thereof. As the operating environment may reach a continuous temperature in the range −20° C. to 150° C., there is also a need to provide a sensor that will remain stable over the operating temperature regime. Moreover, the sensors often used for monitoring have the tendency to drift with time and hence are unstable over a period of time, resulting in incorrect monitoring of health of electrical machines.
Therefore, to assess the condition of the electrical machine, there is a need for an efficient monitoring system that easily and rapidly monitors the health.